Washington (CNN) -- President Barack Obama will nominate Gen. Martin Dempsey, the relatively new Army chief of staff, to be the next chairman of the Joint Chiefs of Staff, several administration officials say.

The term of the current chairman, Adm. Michael Mullen, ends in September.

The officials all warned, however, that since the appointment has not yet been officially announced, there is a chance the president could change his mind. The White House and Pentagon declined to comment on the nomination.

The selection would represent a turn from the conventional wisdom. For some time, Gen. James Cartwright, a four-star Marine who currently is vice chairman of the Joint Chiefs, was the perceived front-runner. But in a 30-minute meeting with Obama on Saturday, before the president left for Europe, Cartwright was told he would not get the job, according to a Defense Department official with direct knowledge of the meeting.

The official declined to be identified because of the sensitivity of discussing White House personnel meetings involving the president.

Cartwright is now expected to submit his retirement papers and conclude his term as vice chairman as scheduled in early August.

Cartwright had long been considered a White House favorite, but had run afoul of other senior officers inside the Pentagon who felt he more than once went behind their backs in offering the president military recommendations and advice on a range of issues, including lower troop levels in Afghanistan.

The Defense Department official who is familiar with Cartwright's thinking says the general was aware of these criticisms, and only offered recommendations when asked by the president.

"There was an impression created he wasn't a team player," said the official, who was offering a defense of Cartwright's actions

"Gen. Cartwright never believed he was a deputy. He believed he had a legal and moral obligation to give the president his best military advice," the source said. "He is not obligated to provide the same advice as everybody else."

The official acknowledged the widespread view many had, however, that Cartwright plays his cards close to the vest inside the Pentagon and often shared little with colleagues about his real thinking.

The official said that before walking into the meeting with the president, Cartwright had made up his mind he would be stepping down, given all the recent controversy.

But the handwriting clearly was on the wall that he was no longer the top choice. The official said neither Defense Secretary Robert Gates nor Mullen had recommended Cartwright for the job as chairman, which meant his nomination by the White House would have been difficult to justify to Congress.

Spokesmen for both declined to publicly comment on any aspect of the chairmanship issue.

Cartwright had also been the subject of an investigation by the department's inspector general over whistle-blower allegations of improper conduct with a junior female officer who fell asleep intoxicated in his hotel room during a business trip. He was cleared of wrongdoing by Navy Secretary Ray Mabus, but the official said Cartwright felt he was the still the subject of a "whispering campaign" after that.

The selection of Dempsey in itself is unusual because he took over as head of the Army only on April 11. But in that time, his outgoing personality has taken hold. Every week, he receives a list of soldiers both in the United States and overseas and calls them to get their direct opinions on life in the Army.

He has also gained attention for his long-standing habit of beginning some of his public speaking events by singing songs such as "New York, New York." On his Facebook page, he recently asked troops to offer their suggestions for music he could play at events where he is speaking.

"Here is a question for the younger soldiers. When I speak at events I like to use videos set to music to help reinforce my message. What song do you think of when you think of our great Army? Only rule: No offensive language," Dempsey wrote. The soldiers responded with suggestions ranging from Toby Keith to Metallica.

His sense of humor has opened Dempsey up for some ribbing as well, like at the ceremony when he took command of the Army.

"His rise to this great height is yet another one of those classic American immigrant success stories," said Army Secretary John McHugh during official remarks. "One can only imagine how different his life might have been had his family not decided to leave New Jersey and move across the river to New York state."

Dempsey has extensive combat experience. He served as the commander of the 1st Armored Division in Baghdad in 2003, and then helped train Iraqi security forces in a subsequent tour of duty in Iraq. He also has served as acting commander of the U.S. Central Command overseeing U.S. military operations in the Middle East, Persian Gulf and Central Asia.

If confirmed by the Senate, Dempsey would be in the key position of being Obama's senior military adviser, overseeing the drawdown of troops in Iraq and Afghanistan while also working with incoming Defense Secretary Leon Panetta, who also still needs to be confirmed by the Senate, in establishing priorities for cutting defense spending.